Boston, Ma - Landlord Is Falsely Claiming Residency In My Apartment To Receive Property Tax Exemption

I moved into a 1BR apartment in Boston this past September, and I noticed the mailbox had my name AND my landlord's name listed on the mailbox. When asked about it, he brushed it off saying sometimes mail gets sent there and we can just ignore it. That being said, I accidentally opened their mail , of what looked to be a bill from the city (I am expecting a bill from the city and assumed this was mine) - it was a property tax statement, to which they were receiving a ~60% tax exemption due to being listed as a resident of the unit.

My question - is this considered fraud? As a tenant , do you suggest I report this? If next lease term, lets say he decides to pass an exorbitant rent increase, can I/should I use this against him to negotiate? Or should I withhold due to the fact that 1) he is otherwise not a problematic landlord (so far), and 2) I technically read his mail which I assume is not totally legal.